Piston cylinder assembly

ABSTRACT

A hydraulic circuit for use in a lift truck having a valve responsive to a difference in the pressures of the fluids on opposite sides of the piston of a piston cylinder assembly. The valve is spring-biased to a first position and movable to a second position when the fluid pressure on one side of a spool within the valve exceeds the fluid pressure on the opposite side of the spool by a value in excess of the value of the force of the spring. The spool, when in its second position, prevents a flow of fluid to one side of the piston. The piston cylinder assembly has a rod connected to one side of the piston and extending out of the cylinder. The rod and cylinder define therebetween an annular fluid transfer passage. An annular seal is connected to the piston and designed to encompass and seal the annular passage when the piston is adjacent the end of the cylinder in which the annular passage is located. The annular passage is sealed to entrap a quantity of fluid between the piston and cylinder to prevent direct contact therebetween. Additional passages communicate the fluid on each side of the piston to the opposite sides of the spool.

United States Patent 1 Neuman Aug. 12, 1975 PISTON CYLINDER ASSEMBLY [75] Inventor: Richard Neuman, Farmington, ABSTRACT 'Mlch' A-hydraulic circuit for use in a lift truck having a [73] A ignee; Eaton Cor oration, Clev l d Ohi valve responsive to a difference in the pressures of the fluids on opposite sides of the piston of a piston cylin- [22] Flled' 1973 der assembly. The valve is spring-biased to a first posi- [21] A N 345,826 tion and movable to a second position when the fluid pressure on one side of a spool within the valve exceeds the fluid pressure on the opposite side of the [52] :LSSI. 91/395, 91431059; Spool by a value in excess of the value Of the force of 51 nt. the springqhe spoohwheninitssecond positionpw [58] Fleld of 262 9 4 vents a flow of fluid to one side of the piston. The pisl/ 0 ton cylinder assembly has a rod connected to one side of the piston and extending out of the cylinder. The [56] References C'ted rod and cylinder define therebetween an annular fluid UNITED STATES PATENTS transfer passage. An annular seal is connected to the 2,319,608 5/1943 Kraut 91/395 piston and designed to encompass and seal the annular 2.321.079 6/19 3 r n ald 1/ passage when the piston is adjacent the end of the cyl- 2556598 6/195l Loewe 91/395 inder in which the annular passage is located. The an- 3- 6/1953 f f 91/395 nular passage is sealed to entrap a quantity of fluid begf tween the piston and cylinder to prevent direct 5 8/1964 zsig 92/8,; contact therebetween. Additional passages communi- 513291055 7/1967 Klaus..:::.:.........................:.:..: 92/85 K F fluid each Side of the Piston the OPPO' site sides of the spool.

Primary Examiner-Paul E. Maslousky 7 Cl 2 D Attorney, Agent, or Firm-Teagno & Toddy aims rawmg lgures I ht 1W 'oenfi'f ti fi r 4H 1 v 4 /A 7 14 v i 7/ *IQI 1\Q 4 W11 gQIliMSFS- l l w w w Z V 4 U M H 9 Ni "i I r. P.) Q Q 5/ W II, s 14-. A?

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates generally to an overload protection device for use on vehicles and, more particularly, to a piston cylinder assembly for use on such vehicles.

2. Description of the Prior Art The problem of preventing vehicles, such as lift trucks, from overturning has been investigated by a number of individuals, see, for example, U.S. Letters Pat. No. 2,774,437 (Remde), 2,767,394 (Arnot et al.), and 3,059,7l (Pien). Several individuals have made use of the fact that the force tending to overturn the lift truck is related to the force exerted on the push rod of one of the piston cylinder assemblies used to tilt the mast. One concept carries this fact further to show that the force on the push rod is directly related to the difference in the pressures of the fluids in the cylinder on opposite sides of the piston in the given piston cylinder assembly. In making use of this concept, the fluid pressures on each side of the piston are transmitted to a pressure responsive valve which prevents further tilting when the moment tending to overturn the lift truck approaches an unsafe value. This concept is set out in U.S. Letters Pat. No. 3,007,593 (Hancock). In order to effectively use the difference in pressure concept, a pressure, other than zero, must be transmitted from the side of the piston having the greatest fluid pressure. Hancock fails to recongize this fact in that the piston of Hancock may contact the end of the cylinder during tilting of the mast causing the fluid pressure from that side of the piston to become zero thereby making the pressure responsive valve ineffective.

SUMMARY OF THE INVENTION The present invention has application to devices such as a counterbalanced vehicle having a mast, boom, arm or other primary load member movable relative to a frame by a piston cylinder assembly interconnecting the primary load member and the frame and means operative to sense the difference in pressure on opposite sides of the piston and transmit this differential pressure signal to a suitable device to preclude further movement of the piston relative to the cylinder.

According to a feature of the invention, the rod of the piston cylinder assembly, as it projects through one end of the cylinder, defines therewith an annular passage encircling the rod and communicating with the exterior of the cylinder and the chamber in the cylinder at the rod side of the piston, and means is provided to seal the annular passage when the piston is near the one end of the cylinder to entrap fluid between the piston and the one end of the cylinder and prevent contact therebetween thereby insuring that a positive pressure signal is available from that side of the piston for transmittal to the pressure sensing means. An annular resilient seal, which encircles the rod, is secured to the one side of the piston and projects toward the one end of the cylinder beyond the piston to encompass and seal the annular opening when the piston approaches the one end of the cylinder.

According to another feature of the invention the annular passage of the piston cylinder assembly is adapted to be connected to a fluid receiving passage in a fluid circuit, and another passage, that is always in communication with the exterior of the cylinder and the fluid in the chamber at the rod end, is provided in the cylinder for transmitting a pressure signal to the pressure sensing means; the other passage and the annular passage form separate and distinct passages from the chamber at the rod end of the cylinder to the exterior of the cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the invention is disclosed in the accompanying drawings, wherein:

FIG. 1 is a schematic plan view of a hydraulic circuit embodying a piston cylinder assembly according to the invention; and I FIG. 2 is a side elevational view, in section, of onehalf of a piston cylinder assembly according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a hydraulic circuit having a conduit 12 interconnecting a pump 14 and a reservoir 16. A conduit 18 connects pump 14 to a port of selector control 20. Another port of selector control 20 is connected to reservoir 16 via conduit 22. Conduits 24 and 26 are also connected to ports of selector control 20. Selector control 20 is operative upon movement to: connect conduit 18 to conduit 26 and conduit 22 to conduit 24; connect conduit 18 to conduit 24 and conduit 22 to conduit 26; and connect conduit 18 to conduit 22.

A piston cylinder assembly 28 has a piston 30 having an annular side 32 partially defining a first chamber 34 in cylinder 36 and a full area side 38 partially defining a second chamber 40 in the cylinder. Conduits 24 and 41, respectively, communicate with first and second chambers 34 and 40 through first and second q d portions 42 and 44. A push rod 46 is connected to annular side 32 of piston 30 and projects out of first end 42 of cylinder 36 through seal 48. A resilient seal 50 is secured to and projects away from annular side 32 of piston 30. When piston 30 arrives at a position proximate first end 42, seal 50 seals conduit 24 and thereby prevents fluid from flowing from first chamber 34 to conduit 24.

A valve 52 includes a spool 54 that is movable between a first and second position in a generally cylindri' cal cavity 56. Spool 54 includes a pair of end portions 58 and 60 that are rigidly interconnected by a reduced section 62. The end portions are in sliding engagement with the cylindrical wall of cavity 56. End portion 58 has an annular side 64 partially defining first chamber 66 in cavity 56 while end portion 60 includes a full area side 68 partially defining second chamber 70 in cavity 56. A pair of axially spaced annular spaces 86 and 88 are located intermediate chambers 66 and 70. Projections 72 are secured to annular side 64 and adapted to contact one surface of a wall 74 that separates chamber 66 from a spring cavity 76 that is located in valve 52. A rod 78 is secured at one end to end portion 58 and projects through an opening in wall 74 into spring cavity 76. An annular seal 80 encircles rod 78 and separates the environment of chamber 66 from that of spring cavity 76. A compression spring 82, under load. encircles rod 78 in spring cavity 76 and has one end contacting a surface of wall 74 and another end contacting a circular disk 84 that is secured to the other end of rod 78.

Spool 54 is illustrated in FIG. 1 in its first position. Annular-spaces 86 and 88 communicate with one another via the annular space around center section 62. Movement of spool 54 to the second position results in the cylindrical surface of end portion 58 sealing annular spaces 86 and 88 from one another. Conduits 26 and 41, respectively, communicate with annular spaces 86 and 88. Spool 54 acts as a valve to allow fluid to flow from conduit 26 around center section 62 to conduit 41 when spool 54 is located in its first position and to prevent fluid from flowing from conduit 26 around center section 62 to conduit 41 when spool 54.is located in its second position. Another conduit 90 communicates with annular space 86 and conduit 26. A one-way check valve 92 located in conduit 90 allows to flow only from annular space 86 to conduit 26.

The pressures of the fluids in chambers 34 and 40 are transmitted via conduits. 94 and 96, respectively, to chambers 66 and 70. The ratio of the area of annular side 32 to the area of full area side 38 of piston 30 is equal to the ratio of the area of annular side 64 to the area of full area side 68 ofspool 54. Movement of spool 54 is governed by the preload and rate of spring 82 and the difference in the pressures of the fluids in chambers 34 and 40. The preload of the spring is governed by the maximum tensile force desired on rod 46 prior to the beginning of movement of spool 54 from its first to its second position and the rate of the spring is governed by theincremental pressure rise desired at full open to full closed position of spool 54.

When the force exerted on the annular side 64 by the.

pressure of the fluid in chamber 66 exceeds the combined force exerted by the pressure of the fluid in chamber 70 on full area side 68 and the preload of spring 82 spool 54 begins to move to the left in FIG. 1 toward its second position. As the force on annular side 64- increases relative to the force on full area side 68, a point is reached when end portion 58 seals annular space 86 from annular space 88.

lf piston 30 contacted first end 42 of cylinder 36 the force exerted onannular side 32 would be transmitted directly to the first end thereby causing the pressure of the fluid in chamber 34 to become zero. In such an instance spool 54 would become unresponsive to the tensile force exerted on rod 46 since the pressure of the fluid in chamber 66 would also be zero. Seal 50 prevents this from happening by sealing passage 24 and entrapping a quantity of fluid between piston 30 and first end 42. The seal is resilient to prevent a noticeable transmittal of force from the piston to the first end. By entrapping a quantity of fluid between the piston and the first end,'increases in the tensile force on rod 46 will result in corresponding increases in the pressure of the fluid in chamber 34 and accordingly increases in the pressure of the fluid in chamber 66.

Looking now at FIG. 2, piston cylinderassembly 28 is illustrated in detail and includes'an annular body portion 98 defining a cavity 100 that is enclosed by first and second ends 42 and 44. Piston 30 is in sliding engagement with the inner cavity defining surface of body portion 98 and includes resilient seals 99 for preventing fluid flow between chambers 34 and 40. Push rod 46 has a shoulder 102 in abutting engagment with piston 30. A nut 104 in in threaded engagement with rod 46 to secure the rod and piston together. A number of resilient seals I06 mountedin first end 42 encircle rod 46. First end 42 includes an annular plate 108 secured to the body portion of first end 42 by a number of screws 110, only one shown. that are circumferentially spaced around rod 46. An annular opening 112 in plate 108 defines an annular passage between rod 46 and plate 108 that communicates with chamber 34 and an annular cavity 114 in first end 42. Annular cavity 114 communicates with conduit 24. Annular seals 116 are located between plate 108 and the body portion of first end 42 to prevent fluid from flowing therebetween. Conduit 94 communicates with chamber 34 via a passage 117 through first end 42. As illustrated, in FIG. 2, passage 117 must be located in a position so that it is never sealed by piston 30.

On .the annular side of piston 30 there is included an annular cavity 1 18 defined by the outer surface of frusturn of a cone. Annular cavity 118 is concentric with rod 46 and diverges in cross-sectional are from left to right in FIG. 2. At the left-hand end of annular cavity 118 there is located an enlarge annular groove having an outer conical surface 120 diverging from right to left in FIG. 2 and beginning at the termination point of the surface defining annular cavity 118. A resilient annular seal 122 conforms to surface 120 and is in abutting engagement with the outer cylindrical surface 128 of rod 46 juxtaposition piston 30. The second end of annular seal 122 projects outwardly into chamber 34 away from the outermost surface 130 of piston 30 and includes a dish-shaped opening 132 converging outwardly from left to right in FIG. 2 and defined by the outer surface of a frustum of a cone. Dish-shaped opening 132 terminates at an outer circular edge 134. The diameter of outer circular edge 134 is greater than the diameter of annular opening 112 in plate 108. The outer cylindrical surface 136 of annular seal 122 is spaced from the defining surface of conical cavity 118.

In operation, selector control 20 is moved to communicate conduits l8 and 26 with one another and conduits 22 and 24 with one another. Fluid is thereby introduced into chamber 40 and removed from chamber 34 causing piston 30 to move to the right in FIG. 2. When piston 30 arrives at a position proximate end 42, outer edge 134 of seal 122 contacts surface 138 of plate 108 thus sealing annular passage 112 from chamber 34. When passage 112 is sealed fluid is no longer permitted to flow out of chamber 34 and further movement of piston 30 to the right in FIG. 2 will result only in an increase in pressure in chamber 34. Seal 122 is free to yield under the force of movement of piston 30 to the right and will eventually compress to conform in part to cavity 118. Due to the mass of material of seal 122 extending beyond surface 130 of piston 30 toward end 42, at no time will surface 130 of piston 30 contact surface 138 of cylinder 36. After seal 122 conforms in part to cavity 118 the remainder of seal 122 extending beyond surface 130 will compress between surfaces 130 and 138. During compression between surfaces 130 and 138 seal 122 tightly grips rod 46 due to the radial forces exerted by the pressure of the fluid in chamber 34. To cause piston 30 to move to the left in FIG. 2 selector control is moved to the position illustrated in FIG. 1. Fluid is forced through conduit 24 against seal 122. Seal 122 gives readily due to the reduced seal surface prcsented by dish-shaped opening 132 allowing fluid to enter chamber 34. Simultaneously, fluid in chamber 40 is free to flow to reservoir l6.via conduit 41 and either past center portion 62 or through check valve 92 into conduit 26.

The circuit of FIG. 1 may be used in the same manner as a portion of the circuit illustrated and described in US. Letters Pat. No. 3,007,593 (Hancock). For exam ple, in FIG. 3 of Hancock, valve 52 of the disclosure can be substituted for valve 16 of Hancock and piston cylinder assembly 28 of the disclosure can be substituted for tilting jack 6 of Hancock. Other connections and substitutions will be obvious to those skilled in the art. Other uses for the circuit are also contemplated.

What is claimed is:

l. A fluid actuated piston cylinder assembly having a fluid supply passage and a fluid receiving passage, for use with a fluid circuit, comprising:

a housing having a body portion intermediate first and second end portions, the body and end portions defining together a cavity;

a piston within the cavity in sliding engagement with the body portion and dividing the cavity into first and second chambers, both chambers containing a fluid, the first chamber being partially defined by the first end portion;

a rod connected to the piston and extending out of the cavity through the first end portion, the first end portion and the rod defining therebetween an annular passage adapted to be the sole communication between the first chamber and the fluid receiving passage; and resilient member encircling the rod and having a first end engaging the piston and a second end projecting away from the piston towards the first end of the housing, the circumferential portion of the second end of the resilient member being of a size to encompass the annular passage and having a surface area normal to the axis of said resilient member that varies along the axis of said resilient member from a relatively small surface cross-sectional area at said second end to the full cross-sectional area of said resilient member at an axial position intermediate said first and second ends thereby presenting a sealing surface when abutting the first end portion of the cylinder which is substantially smaller in cross-sectional area than the total crosssectional area of said resilient member;

whereby when the piston approaches a position proximate the first end the resilient member seals the annular passage entrapping a quantity of fluid between the piston and the fluid end, thereby ensuring that a fluid pressure is maintained within the first chamber.

2. A piston cylinder assembly according to claim I further comprising means defining a sensing passage in the housing communicating with the first chamber and the exterior of the housing, the sensing passage being located for communication with entrapped quantities of fluid.

3. A piston cylinder assembly according to claim 1 wherein said arrival responsive means is further operative to allow the flow of fluid from said fluid receiving passage to said first chamber when the differential pressure between said fluid receiving passage and said first chamber is a minor fraction of the absolute pressure in said first chamber.

4. A piston cylinder assembly comprising:

a housing having a body portion intermediate first and second end portions, the body and end portions together defining a cavity;

a piston within the cavity in engagement with the body portion and mounted for movement between the cavity defining surfaces of the end portions;

a rod connected to the piston and extending out of the cavity through the first end portion, the first end portion and the rod defining therebetween an annular passage in communication with the cavity and the exterior of the housing;

an annular resilient member encircling the rod and having first and second ends, with the first end engaging the piston, and the second end projecting away from the piston toward the first end portion to contact the cavity defining surface of the first end portion when the piston is located a given distance away from the first end portion, and having a cross-sectional area which encompasses the portion of the annular passage communicating with the cavity and having a surface area normal to the axis of said resilient member that varies along the axis of said resilient member from a relatively small surface cross-sectional area at said second end to the full cross-sectional area of said resilient member at an axial position intermediate said first and second ends to maintain a quantity of fluid between the piston and the first end portion upon contact between the second end of the resilient member and the first end portion to prevent direct contact between the piston and the first end portion and to form a minimal area seal encompassing said annular passage.

5. A piston cylinder assembly according to claim 4 wherein:

the piston defines an radially outwardly extending annular opening;

the resilient member is substantially cylindrical in configuration; and

the first end of the resilient member has an annular shoulder in mating engagement with the annular opening in the piston.

6. A piston cylinder assembly according to claim 4 wherein:

a dish-shaped opening is located within the second end of the resilient member;

the annular passageis circular; and

the second end has a circular outer edge having a diameter greater than the diameter of the annular passage and defining the outer boundary of the dish-shaped opening.

7. A piston cylinder assembly according to claim 4 further comprising means defining a sensing passage in the housing communicating with the first chamber and the exterior of the housing, the passage being separate from the annular passage and located to communicate with the space between the piston and the first end por- 

1. A fluid actuated piston cylinder assembly having a fluid supply passage and a fluid receiving passage, for use with a fluid circuit, comprising: a housing having a body portion intermediate first and second end portions, the body and end portions defining together a cavity; a piston within the cavity in sliding engagement with the body portion and dividing the cavity into first and second chambers, both chambers containing a fluid, the first chamber being partially defined by the first end portion; a rod connected to the piston and extending out of the cavity through the first end portion, the first end portion and the rod defining therebetween an annular passage adapted to be the sole communication between the first chamber and the fluid receiving passage; and a resilient member encircling the rod and having a first end engaging the piston and a second end projecting away from the piston towards the first end of the housing, the circumferential portion of the second end of the resilient member being of a size to encompass the annular passage and having a surface area normal to the axis of said resilient member that varies along the axis of said resilient member from a relatively small surface cross-sectional area at said second end to the full cross-sectional area of said resilient member at an axial position intermediate said first and second ends thereby presenting a sealing surface when abutting the first end portion of the cylinder which is substantially smaller in cross-sectional area than the total cross-sectional area of said resilient member; whereby when the piston approaches a position proximate the first end the resilient member seals the annular passage entrapping a quantity of fluid between the piston and the fluid end, thereby ensuring that a fluid pressure is maintained within the first chamber.
 2. A piston cylinder assembly according to claim 1 further comprising means defining a sensing passage in the housing communicating with the first chamber and the exterior of the housing, the sensing passage being located for communication with entrapped quantities of fluid.
 3. A piston cylinder assembly according to claim 1 wherein said arrival responsive means is further operative to allow the flow of fluid from said fluid receiving passage to said first chamber when the differential pressure between said fluid receiving passage and said first chamber is a minor fraction of the absolute pressure in said first chamber.
 4. A piston cylinder assembly comprising: a housing having a body portion intermediate first and second end portions, the body and end portions together defining a cavity; a piston within the cavity in engagement with the body portion and mounted for movement between the cavity defining surfaces of the end portions; a rod connected to the piston and extending out of the cavity through the first end portion, the first end portion and the rod defining therebetween an annular passage in communication with the cavity and the exterior of the housing; an annular resilient member encircling the rod and having first and second ends, with the first end engaging the piston, and the second end projecting away from the piston toward the first end portion to contact the cavity defining surface of the first end portion when the piston is located a given distance away from the first end portion, and having a cross-sectional area which encompasses the portion of the annular passage communicating with the cavity and having a surface area normal to the axis of said resilient member that varies along the axis of said resilient member from a relatively small surface cross-sectional area at said second end to the full cross-sectional area of said resilient member at an axial position intermediate said first and second ends to maintain a quantity of fluid between the piston and the First end portion upon contact between the second end of the resilient member and the first end portion to prevent direct contact between the piston and the first end portion and to form a minimal area seal encompassing said annular passage.
 5. A piston cylinder assembly according to claim 4 wherein: the piston defines an radially outwardly extending annular opening; the resilient member is substantially cylindrical in configuration; and the first end of the resilient member has an annular shoulder in mating engagement with the annular opening in the piston.
 6. A piston cylinder assembly according to claim 4 wherein: a dish-shaped opening is located within the second end of the resilient member; the annular passage is circular; and the second end has a circular outer edge having a diameter greater than the diameter of the annular passage and defining the outer boundary of the dish-shaped opening.
 7. A piston cylinder assembly according to claim 4 further comprising means defining a sensing passage in the housing communicating with the first chamber and the exterior of the housing, the passage being separate from the annular passage and located to communicate with the space between the piston and the first end portion. 